1. Field of the Invention
The present invention relates generally to the field of devices for supporting and transferring printed sheets from one printing press station to another. More specifically the present invention relates to a transfer structure such as a cylinder which is wrapped first in a fiberglass belting. The belting is preferably abraded with a wire brush to raise fibers, and then wrapped in a ridged netting material such as ultra-soft cotton fabric, which is fit snugly around the cylinder, but not so tightly as to pull the ridging out of the netting material, for supporting and transferring a freshly printed sheet. The ridges serve to engage the sheet much like teeth while cushioning and yielding as the freshly printed surface of the sheet bears against the ridges to prevent smearing or other marring of wet ink. The cylinder preferably includes a conveying surface with a matte finish to minimize slipping of the netting material relative to the conveying surface.
The transfer cylinder preferably includes releasibly interconnected first and second longitudinal cylinder half portions, each half portion having an arched outer shell segment forming a portion of a sheet conveying surface and first and second shell segment half hub structures secured respectively within the first and second longitudinal cylinder half portions, the half hub structures including delivery shaft receiving structure and hub interconnection elements releasibly joining the first and second half hub structures together.
A method is also provided of covering a conveying surface of a transfer structure such as a cylinder with a fiberglass blanket, abrading the blanket with a wire brush to raise fibers, wrapping the blanket with a yielding ridged netting material, and tightening the netting material to a tension level just short of pulling out the ridges, then causing the transfer structure to move relative to a printing press station in such a way as to pick up the printed product and carry it to another such station.
2. Description of the Prior Art
There have long been transfer structures for supporting and conveying freshly printed sheets of material from one station of a printing press to the next station. A key design objective has been for the structure to sufficiently grip the sheet to move it without smearing or smudging the wet ink on its surface.
One such prior transfer structure is that of DeMoore, U.S. Pat. No. 4,402,267, issued on Sep. 6, 1983. DeMoore teaches a method and apparatus for handling printed sheet material, including a skeleton transfer cylinder. The cylinder is coated with a fluorocarbon composite material to provide a cushioning effect for the sheets. The cylinder is wrapped in a piece of fabric which is secured loosely for the intended purpose of preventing the transfer of wet ink from one sheet to a successive sheet. The fabric is treated with an absorbance retarding substance such as SCOTCHGARD.TM.. A problem with DeMoore is that this structure is not well suited to small printing presses. Another problem is that loose, flopping fabric can bunch and wear quickly. The flopping fabric has a tendency to slap the tail end of the impression cylinder and create an ink build-up on the tail end of the transfer cylinder, and the netting thereon, which causes marring of the surface of the next sheet of paper that is transferred.
Ellis, U.S. Pat. No. 1,231,141, issued on Jun. 26, 1917, discloses a fabric for printers' blankets and other purposes. Ellis describes a multiple layer blanket for packing impression cylinders of newspaper presses. The outer layer face is felt covered. It appears unclear whether the blanket material is intended to fit tightly or loosely over an impression cylinder. A problem with Ellis is that felt can mar a freshly printed surface. Another problem is that the multiple layer construction would likely be costly.
Goldsmith, U.S. Pat. No. 944,607, issued on Dec. 28, 1909, teaches tile coating machinery. Goldsmith includes a coating roll having ribbed rubber periphery enclosed within a foraminous metallic sleeve. The foraminous sleeve is loosely mounted on the roll. A problem with Goldsmith is that the metallic sleeve would likely damage printed sheets and mar wet ink on their surfaces.
Boucher, U.S. Pat. No. 1,152,596, issued on Sep. 7, 1915, reveals a covering for use on a suction-roll which is used on paper making machines. The covering consists of a coarse knit sleeve, preferably knit from wool worsted yarn and adapted to be stretched over the suction roll. A problem with Boucher is that the coarse sleeve would likely be too rigid to convey freshly inked sheets without marring. Another problem is that these sleeves might slip on a typical smooth surfaced transfer cylinder.
Dickerson, U.S. Pat. No. 3,261,288, issued on Jul. 19, 1966, discloses an anti-smear jacket for a printing press transfer drum. Dickerson uses a series of elongated resilient spacing elements or strips on the outside of a transfer cylinder instead of fabric. A problem with Dickerson is that the hard, resilient strips could mar wet ink on a sheet.
McGibbon, U.S. Pat. No. 4,023,967, issued on May 17, 1977, reveals an electrophotographic liquid development method in which a uniform substantial interface contact is maintained. McGibbon uses a roller device having a core loosely circumscribed axially with a flexible sleeve, with a space between the core and the sleeve being substantially uniform. This space is filled with a curable plastic foam material to obtain a uniform contact and nip width when in rotational contact with a cooperating surface. A problem with McGibbon is that the loose mounting of the sleeve on the core promotes marring and rapid sleeve wear. Another problem is that the resilient full sleeve contact can also increase the likelihood of marring.
An operation manual, entitled "Heidelberg M-Offset Multicolour-Perfector", dated October 1981, discloses a loosely mounted glass-bead blanket mounted on a transfer cylinder. A wire gauze material is used instead of a fabric. The problems presented by Heidelberg are essentially those of Dickerson.
Hartmann, U.S. Pat. No. 1,255,603, filed Feb. 3, 1916, discloses a printing cloth for presses where the cloth is tensioned around a printing roller or cylinder to convey printed stock. The outer conveying surface of the cylinder is grooved. A problem with Hartmann is that the cloth itself is not stated to be ridged or grooved to engage and convey the printed stock, which makes smearing and other marring likely.
U.S. Pat. No. 5,415,098, issued on May 16, 1995 to the present applicant, discloses a method and apparatus for handling sheet material using ridged netting. This prior apparatus placed ridged netting directly onto the transfer cylinder, making it necessary for the cylinder contact surface to be rough beyond the natural unfinished texture to prevent circumferential movement of the netting. The prior apparatus also required the conventional amount of effort to remove and reinstall the cylinder on the chain delivery shaft.
It is thus an object of the present invention to provide a method and apparatus for transferring and supporting freshly printed sheets between printing press stations without marring the wet ink.
It is another object of the present invention to provide such a method and apparatus which is well suited for use on many of the smaller printing presses.
It is still another object of the present invention to provide such a method and apparatus which operate with minimal wear and maximum longevity.
It is a further object of the present invention to provide such an apparatus including a transfer cylinder which is quickly and easily removed and remounted.
It is finally an object of the present invention to provide such a method and apparatus which are reliable and produce a printed sheet product of consistent high quality.